Numerous methods and materials exist for the construction of retaining walls. Such methods include the use of natural stone, poured in place concrete, masonry, and landscape timbers or railroad ties. In recent years, segmental concrete retaining wall units which are dry stacked (i.e., built without the use of mortar) have become a widely accepted product for the construction of retaining walls. Examples of such products are described in U.S. Pat. No. Re. 34,314 (Forsberg '314) and U.S. Pat. No. 5,294,216 (Sievert). Such products have gained popularity because they are mass produced, and thus relatively inexpensive. They are structurally sound, easy and relatively inexpensive to install, and couple the durability of concrete with the attractiveness of various architectural finishes.
The retaining wall system described in Forsberg '314 has been particularly successful because of its use of block design that includes, among other design elements, a unique pinning system that interlocks and aligns the retaining wall units, allowing structural strength and efficient rates of installation. This system has also shown considerable advantages in the construction of larger walls when combined with the use of geogrid tie-backs hooked over the pins, as described in U.S. Pat. No. 4,914,876 (Forsberg).
The construction of modular concrete retaining walls as described in Forsberg involves several relatively simple steps. First, a leveling pad of dense base material or unreinforced concrete is placed, compacted and leveled. Second, the initial course of blocks is placed and leveled. Two pins are placed in each block into the pin holes. Third, core fill material, such as crushed rock, is placed in the cores of the blocks and spaces between the blocks to encourage drainage and add mass to the wall structure. Fourth, succeeding courses of the blocks are placed in a “running bond” pattern such that each block is placed between the two blocks below it. This is done by placing the blocks so that the receiving cavities of the bottom of the block fit over the pins that have been placed in the units in the course below. As each course is placed, pins are placed in the blocks, the blocks are core filled with drainage rock, and the area behind the course is backfilled and compacted until the wall reaches the desired height.
If wall height or loading conditions require it, the wall structure may be constructed using reinforced earth techniques such as geogrid reinforcement, geosynthetic reinforcement, or the use of inextensible materials such as steel matrices. The use of geogrids are described in U.S. Pat. No. 4,914,876 (Forsberg). After placement of a course of blocks to the desired height, the geogrid material is placed so that the pins in the block penetrate the apertures of the geogrid. The geogrid is then laid back into the area behind the wall and put under tension by pulling back and staking the geogrid. Backfill is placed and compacted over the geogrid, and the construction sequence continues as described above until another layer of geogrid is called for in the planned design. The use of core fill in the blocks is known to enhance the wall system's resistance to pull out of the geogrid from the wall blocks when placed under pressure.
Existing segmental wall block designs have proven quite versatile, but have limitations in constructing certain structures. A common design detail for retaining wall structures is to include a fence or guardrail at the top of the retaining wall. Many segmental wall designs are not able to accommodate the anchoring posts for such structures. Similarly, it is not always feasible to extend geosynthetic reinforcement behind a wall. This may occur due to the presence of a structure or a property line immediately behind the wall. Most existing modular walls blocks cannot be constructed through the use of grout and rebar reinforcement.
There is a need for a retaining wall block that improves on the Forsberg design. Since the blocks are usually placed through manual labor, it would be desirable to decrease the weight of the Forsberg design without compromising the performance characteristics of the block. Because the placement of core fill is an important factor influencing wall construction efficiency, it would be desirable to improve the ease with which core fill may be placed. It would also be desirable to improve the Forsberg blocks' ability to resist pull out of geosynthetic reinforcement placed between courses of the blocks. It would also be desirable to have a wall block design that would allow construction of such common construction details as the placement of guardrail posts or fence posts at the top of the wall, or the provision of pilasters for aesthetic or other purposes. It would also be desirable to provide a block that would allow the wall to be reinforced with rebar and concrete grout rather than soil reinforcement.